(1) Field of the Invention
The present invention relates to a method of and apparatus for plating a board or plate, and more particularly to a method of and apparatus for plating a printed circuit board.
(2) Description of the Related Art
Generally, in a conventional method for plating a board or plate, a metal film or layer is formed on a surface of an insulating material by a non-electrolytic plating process for establishing conductivity in the material. A conventional method for plating a board such as a printed circuit board employs a procedure wherein a through hole is formed at an appropriate location in a surface of a copper plated epoxy resin laminated board and a catalytic liquid is caused to be absorbed in an inner wall of the through hole, followed by a non-electrolytic copper plating process for copper-plating the overall surface including a surface of the inner wall of the through hole. In this case, through the through hole thus formed, the electrical connection is established between a front and a back side of the copper plated laminate board. Where a multi-layer wiring board is provided with a non-through hole, similarly a metal film is formed in an inner wall of the non-through hole whereby the interconnection between the metal film on the surface and the inner wiring layer(s) of the multi-layer wiring board is established.
In a conventional non-electrolytic copper plating method, a process for removing bubbles in a vessel in which an inner wall of a through hole or a non-through hole is plated widely uses a combination of swinging and vibration processes.
FIG. 1 is a schematic sectional view of a plating device for describing a conventional method for plating a printed circuit board.
As shown in FIG. 1, a jig 2 carrying a printed circuit board 6 is attached to a supporting body 3 which is connected to a vibration and swing oscillator. The supporting body 3 is caused to be vibrated and swung in a state in which the jig 2 hangs from the supporting body 3 and is immersed in a plating liquid 7 within the vessel 1. Consequently, the bubbles attached to a surface of the printed circuit board 6 or to an inside wall of the through hole or the non-through hole provided in the printed circuit board are removed or expelled and thereafter the plating of a conductive film thereon is effected.
In the conventional method for plating a printed circuit board as described above, as shown in FIGS. 2A and 2B, a part of the bubble existing in the non-through hole is removed due to the vibration and swinging actions but, because of the pressure from the plating liquid 7, the remaining portion of the bubble under pressure in the non-through hole remains in place. This causes problems that an unevenly plated film or incompletely plated film results and that interlayer wirings to be connected to the surface metal layer through the metal film formed inside the non-through hole inevitably become unstable.
Furthermore, in the case where, in order to cope with high density wirings, the diameter of the non-through hole is made small thereby increasing a ratio, i.e., an aspect ratio, between the depth and the diameter of the non-through hole, it becomes impossible to form the plating film inside the non-through hole, in which case the connection between the interlayer wiring layers and the metal films on the surfaces cannot be established.
The above problems or defects in the conventional plating method are to be solved by the present invention.